Oil, gas, water and geothermal wells are typically drilled with a drill bit connected to a hollow drill string which is inserted into a well casing cemented in the well bore. A drilling head is attached to the well casing, wellhead or to associated blowout preventer equipment, for the purposes of sealing the interior of the well bore from the surface and facilitating forced circulation of drilling fluid through the well while drilling or diverting drilling fluids away from the well. Drilling fluids include, but are not limited to, water, steam, drilling muds, air, and other gases.
In the forward circulation drilling technique, drilling fluid is pumped downwardly through the bore of the hollow drill string, out the bottom of the hollow drill string and then upwardly through the annulus defined by the drill string and the interior of the well casing, or well bore, and subsequently out through a side outlet above the well head. In reverse circulation, a pump impels drilling fluid through a port, down the annulus between the drill string and the well casing, or well bore, and then upwardly through the bore of the hollow drill string and out of the well.
Drilling heads typically include a stationary body, often referred to as a bowl, which carries a rotatable spindle such as a bearing assembly, rotated by a kelly apparatus or top drive unit. One or more seals or packing elements, often referred to as stripper packers or stripper rubbers, is carried by the spindle to seal the periphery of the kelly or the drive tube or sections of the drill pipe, whichever may be passing through the spindle and the stripper rubber, and thus confine or divert the core pressure in the well to prevent the drilling fluid from escaping between the rotating spindle and the drilling string.
As modern wells are drilled ever deeper, or into certain geological formations, very high temperatures and pressures may be encountered at the drilling head. These rigorous drilling conditions pose increased risks to rig personnel from accidental scalding, burns or contamination by steam, hot water and hot, caustic well fluids. There is a danger of serious injury to rig workers when heavy tools are used to make a stripper rubber connection at the drilling head. The connection should be made quickly and achieve a fluid tight seal.
Rotating blowout preventers and diverters are well known to those of ordinary skill in the art of well pressure control. Rotation of the diverter/preventer is facilitated by a sealing engaged bearing assembly through which the drill string rotates relative to the stationary bowl or housing in which the bearing assembly is seated. Typically, a rubber O-ring seal, or similar seal, is disposed between the stripper rubber and the bearing assembly to improve the fluid-tight connection between the stripper rubber and the bearing assembly.
Pressure control is achieved by means of one or more stripper rubbers connected to the bearing assembly and disposed around the drill string. At least one stripper rubber rotates with the drill string. Stripper rubbers typically taper downward and include rubber or other elastomeric substrate so that the downhole pressure pushes up on the rubber, pressing the rubber against the drill string to achieve a fluid-tight seal. Stripper rubbers often further include a metal insert that provide support for bolts or other attachment means and which also provide a support structure to minimize deformation of the rubber cause by down hole pressure forces acting on the rubber.
Stripper rubbers are connected or adapted to equipment of the drilling head to establish and maintain the pressure control seal around a down hole tubular (i.e., a drill string). It will be understood by those skilled in the art that a variety of means are used to attach a stripper rubber to associated drilling head equipment. Such attachment means include bolting from the top, bolting from the bottom, screwing the stripper rubber directly onto the equipment via cooperating threaded portions on the top of the stripper rubber and the bottom of the equipment, and clamps.
It will be understood that, depending on the particular equipment being used at a drilling head, a stripper rubber at one well may be connected to equipment specific to that well while at another well a stripper rubber is connected to different equipment. For example, at one well the stripper rubber may be connected to the bearing assembly while at another well the stripper rubber may be connected to an inner barrel or an accessory of the drilling head. While the present disclosure is made here in relation to connecting the stripper rubber to the bearing assembly, it will be evident that the disclosure contemplates connection of the stripper rubber to any selected equipment of the drilling head.
It is common practice to tighten the bolts or screws of the connection with heavy wrenches and sledge hammers. The practice of using heavy tools to tighten a bolt, for example, can result in over-tightening, to the point where the threads or the bolt head become stripped. The results of over-tightening include stripped heads, where the bolt or screw cannot be removed, or stripped threads, where the bolt or screw has no grip and the connection fails. Both results are undesirable.
Even worse, vibration and other drilling stresses can cause bolts or screws to work themselves loose and fall out. If one or more falls downhole, the result can be catastrophic. The drill bit can be ruined. The entire drillstring may have to tripped out, and substantial portions replaced, including the drill bit. If the well bore has been cased, the casing may be damaged and have to be repaired.
Drilling head assemblies periodically need to be disassembled to replace stripper rubbers or other parts, lubricate moving elements and perform other recommended maintenance. In some circumstances, stripped or over tightened bolts or screws make it very difficult if not impossible to disengage the stripper rubber from the drilling head assembly to perform recommended maintenance or parts replacement.
Therefore, a stripper rubber assembly that that overcomes above-mentioned and other known and yet to be discovered drawbacks associated with prior art stripper rubber assemblies individually and, optionally, in combination with oil field drilling equipment (e.g., rotating control head, rotating blowout preventor and/or the like) would be advantageous, desirable and useful.